In installation of gathering lines at sea which extend from submerged well head production equipment to a collection facility, it is necessary to install couplings. Often the collection pipe is welded in strings on the surface and coated with concrete weight material to cause it to sink. The surface welded connections cannot be used for the entirety of the length of the line from origin to destination, and it is necessary to install a coupling which is attached mechanically. It is the sort of coupling which can be installed normally only once, and its correct installation is necessary initially. The coupling must be fluid tight and not require service or checking after installation.
The present invention is a coupling which has these virtues. It is a single coupling which isolates the mechanical coupling of pipe from fluid coupling. It incorporates a mechanical coupling which bears up under loading placed on it, and has a separate fluid seal coupling which is not inflicted with the substantial mechanical load carried by the mechanical coupling. The coupling apparatus finds application at other locations such as on land.